Thermo siphons are well known and used in many different cooling applications. One of these applications is to use a thermo siphon for the cooling of electronic equipment. Since a thermo siphon is a very effective cooling device that requires very, little or even no maintenance it is very useful in applications where the heat load source is isolated and not easily reached. One such application is in telecommunications where radio remote units in wireless telecommunication solutions require high radio capacity which means that these units also becomes a heat load that requires cooling. In these radio remote units more than 60% of the heat load comes from power amplifier components. To keep the hot spots temperature on an acceptable level requires high efficient cooling.
Examples of different thermo siphon configurations for cooling electronic components can be found in patent publications, e.g. US 2007/0242438, U.S. Pat. No. 5,859,763, and U.S. Pat. No. 6,097,597.
U.S. Pat. No. 6,230,788 provides an example showing a thermo siphon based on a channel with heat fins mounted on the channel. Heat from a hot place transfers to upper part of equipments via thermo siphon channels and is distributed to the number of heat fins, where all fins together build up a heat sink.
Japanese Patent Application JP200091482 illustrates (in machine translation) a condenser for semiconductor devices. A member partitions a boiling part and a condensing part and joins a steam passage composition and a refrigerant passage composition. Natural circulation is used and one way is made to circulate through a refrigerant. An optional large-sized fin is attached in modules by screws to the condensing part after heat-conduction grease has been applied. The thermal contact resistance is reduced by dividing the large-sized fin into a plurality of smaller ones.
PCT International Application WO2005088714 demonstrates a cold plate and method of making the same. One or more interior fins or flow channels are machined into the interior (as mounted) of the basic and/or the cover member. The cold plate has a base member and a cover member connected thereto by friction stir welding.
PCT International Application WO2004106822 describes a thin-plate-type cooling device of heat of an external heat source contacting a cooling device is dissipated using the latent heat during phase transition. The cooling device relies upon capillary action for the circulation of the coolant. In case there are gas bubbles in the coolant liquid state reaching an evaporation section, there is a concern that the dry-out phenomenon by which the coolant in the liquid state is exhausted occurs in the evaporation section. In order to prevent dry-out of coolant, the device comprises a cavity for containing a gaseous coolant which has not been condensed formed on an inside wall of coolant circulation loop adjacent to an evaporation section. The thin-plate-type cooling device comprises a lower plate and an upper plate. The evaporation section may be formed only on the lower plate. In embodiments, one or more first cavities in the upper plate provide the space where the coolant in the gas state which has not been condensed may be contained. The upper plate is formed by the same or different material as the lower plate. The one or more cavities prevent the coolant in the gas state which has not been condensed in the condensation section from being bubbles in the coolant in the liquid state.
Capillary action may be achieved by a mesh as is commonly applied in e.g. vapor chambers. The orientation of a vapor chamber is of little importance due to capillary forces providing transportation of coolant also in direction opposite of direction of gravity forces. FIG. 1 illustrates schematically how heat may be spread in various directions from a cross-section view of a vapor chamber. A liquid evaporates in a heat zone (101) and the vapor spreads in the interior (102) of the vapor chamber and hits the walls covered by a wick structure lining (103) where the vapor condenses and is transports in direction towards the heat zone by capillary forces.
FIG. 2 illustrates schematically a two-layer mesh (201), (202) of a wick structure having different pore sizes of the first (201) and second (202) layers.
US Patent Application US20020062648 discloses an apparatus for dense chip packaging using heat pipes. A vapor travels to the condenser region via vapor channels and is condensed to a fluid once again by transferring heat from the vapor to a heat sink. The condensed fluid is then returned to the evaporator region by way of capillary forces and capillaries formed in a capillary structure. The capillaries formed in the capillary structure have tree-like or fractal geometry.
Using of imbedded channels or comprising heat pipes of prior art requires a complicated manufacturing process and a number of channels, thus causing a high price for the final prior art product due to material price and the manufacturing process.
A thermo siphon with a heat sink has a better temperature distribution than just a heat sink but it is in prior art also a complicated and quite expensive unit.